I used to think that one string was optimal; until I had a single cell failure take out an entire system for weeks. (try operating a 24 v system at 22v! ) I now think that 2 parallel strings is optimum, 3 is OK, and 4 is max. At 4 parallel strings, we start spending more time looking to make sure all connectors are the same exact length etc. to insure equal operation. But of course how do you account for varying internal resistance of the batteries......?? I've done 4 parallel strings at 144 DC of sealed batteries on an electric vehicle, but we were very careful with our resistances, I even switched to smaller wire, on closer strings, and calculated out the exact resistance, so all strings were theoretically equal. This set actually just died, but achieved its manufacturer's predicted cycle life. (B&B battery, 350 cycles to 80% DOD) So if you're careful, 4 strings can work well. Worst I've seen was 20 golf carts paralleled in a 12 v system, (10 strings) and they didn't pull the main connections from across the set, just connected to one end. The results were very predictable, with the furthest batteries being chronically under charged, and the closest ones being over cycled to a premature death.
Ray Walters On Dec 1, 2009, at 11:28 AM, [email protected] wrote: > You gotta wonder about why the customer bought such a battery layout, or why > the installer sold that kind of configuration (which ever it was) with so > many small batteries. We would never recommend going over 2 parallel banks, > but sometimes the "customer knows best...". >
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